U.S. patent number 10,989,873 [Application Number 16/663,696] was granted by the patent office on 2021-04-27 for waveguide crossings having arms shaped with a non-linear curvature.
This patent grant is currently assigned to GLOBALFOUNDRIES U.S. INC., KHALIFA UNIVERSITY OF SCIENCE AND TECHNOLOGY. The grantee listed for this patent is GLOBALFOUNDRIES U.S. Inc., KHALIFA UNIVERSITY OF SCIENCE AND TECHNOLOGY. Invention is credited to Yusheng Bian, Sujith Chandran, Marcus Dahlem, Ajey Poovannummoottil Jacob.
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United States Patent |
10,989,873 |
Jacob , et al. |
April 27, 2021 |
Waveguide crossings having arms shaped with a non-linear
curvature
Abstract
Structures for a waveguide crossing and methods of fabricating a
structure for a waveguide crossing. A waveguide crossing includes a
central section and an arm positioned between a waveguide core and
the central section. The arm and the waveguide core are aligned
along a longitudinal axis. The arm is coupled to the waveguide core
at a first interface, and the arm is coupled to a portion of the
central section at a second interface. The arm has a first width at
the first interface, a second width at the second interface, and a
third width between the first interface and the second interface.
The third width is greater than either the first width or the
second width.
Inventors: |
Jacob; Ajey Poovannummoottil
(Watervliet, NY), Bian; Yusheng (Ballston Lake, NY),
Chandran; Sujith (Abu Dhabi, AE), Dahlem; Marcus
(S. M. Feira, PT) |
Applicant: |
Name |
City |
State |
Country |
Type |
GLOBALFOUNDRIES U.S. Inc.
KHALIFA UNIVERSITY OF SCIENCE AND TECHNOLOGY |
Santa Clara
Abu Dhabi |
CA
N/A |
US
AE |
|
|
Assignee: |
GLOBALFOUNDRIES U.S. INC.
(Santa Clara, CA)
KHALIFA UNIVERSITY OF SCIENCE AND TECHNOLOGY (Abu Dhabi,
AE)
|
Family
ID: |
1000004453129 |
Appl.
No.: |
16/663,696 |
Filed: |
October 25, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G02B
6/125 (20130101); G02B 6/12002 (20130101); G02B
6/1228 (20130101); G02B 2006/12061 (20130101); G02B
2006/12097 (20130101) |
Current International
Class: |
G02B
6/12 (20060101); G02B 6/125 (20060101); G02B
6/122 (20060101) |
Field of
Search: |
;385/28 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Sacher et al., "Tri-layer silicon nitride-on-silicon photonic
platform for ultra-low-loss crossings and interlayer transitions",
.COPYRGT. 2017 Optical Society of America. cited by applicant .
Bock et al., "Subwavelength grating crossings for silicon wire
waveguides", .COPYRGT.2010 Optical Society of America. cited by
applicant .
Ma et al., "Ultralow loss single layer submicron silicon waveguide
crossing for SOI optical interconnect", .COPYRGT. 2013 Optical
Society of America. cited by applicant .
Zhang et al., "A compact and low-loss silicon waveguide crossing
for O-band optical interconnect", Proc. SPIE 8990, Silicon
Photonics IX, 899002 (Mar. 8, 2014). cited by applicant .
Bogaerts et al., "Low-loss, low-cross-talk crossings for
silicon-on-insulator nanophotonic waveguides", .COPYRGT. 2007
Optical Society of America. cited by applicant .
Jones et al., "Ultra-low crosstalk, CMOS compatible waveguide
crossings for densely integrated photonic interconnection
networks", .COPYRGT. 2013 Optical Society of America. cited by
applicant .
Shang et al., "Low-loss compact multilayer silicon nitride platform
for 3D photonic integrated circuits" .COPYRGT. 2015 Optical Society
of America. cited by applicant.
|
Primary Examiner: Blevins; Jerry M
Attorney, Agent or Firm: Thompson Hine LLP Canle;
Anthony
Claims
What is claimed is:
1. A structure comprising: a first waveguide core; and a first
waveguide crossing including a central section and a first arm
positioned between the first waveguide core and the central
section, the first arm and the first waveguide core aligned along a
first longitudinal axis, the first arm coupled to the first
waveguide core at a first interface, and the first arm coupled to a
first portion of the central section at a second interface, wherein
the first arm has a first width at the first interface, a second
width at the second interface, and a third width between the first
interface and the second interface, the third width is greater than
the first width, and the third width is greater than the second
width.
2. The structure of claim 1 wherein the first width is less than
the second width.
3. The structure of claim 1 wherein the first arm has a side
surface with a curvature defined by a cosine function.
4. The structure of claim 3 wherein the first arm includes a first
section and a second section, the first section has a first length
that is dependent on a first ratio of the first width to the third
width, and the second section has a second length that is dependent
on a second ratio of the second width to the third width.
5. The structure of claim 1 wherein the first width and the second
width are unequal, and the third width is asymmetrically located
along the first longitudinal axis between the first interface and
the second interface.
6. The structure of claim 1 wherein the first width and the second
width are equal, and the third width is symmetrically located along
the first longitudinal axis between the first interface and the
second interface.
7. The structure of claim 1 further comprising: a second waveguide
core, wherein the first waveguide crossing includes a second arm
with a third interface coupled to the second waveguide core and a
fourth interface coupled to a second portion of the central
section, the second arm having a fourth width at the third
interface, a fifth width at the fourth interface, and a sixth width
between the third interface and the fourth interface, the sixth
width greater than the fourth width, and the sixth width greater
than the fifth width.
8. The structure of claim 7 wherein the second arm and the second
waveguide core are aligned along the first longitudinal axis.
9. The structure of claim 7 wherein the first width is equal to the
fourth width, the second width is equal to the fifth width, and the
third width is equal to the sixth width.
10. The structure of claim 7 wherein the first arm has a first side
surface with a first curvature defined by a first cosine function,
the second arm has a second side surface with a second curvature
defined by a second cosine function, and the first curvature is
substantially identical to the second curvature.
11. The structure of claim 7 wherein the first arm has a first side
surface with a first curvature defined by a first non-linear
function, and the second arm has a second side surface with a
second curvature defined by a second non-linear function, and the
second curvature that is substantially identical to the first
curvature.
12. The structure of claim 7 wherein the first waveguide crossing
includes a third arm coupled to a third portion of the central
section and a fourth arm coupled to a fourth portion of the central
section, and the first arm, the second arm, the third arm, and the
fourth arm have respective side surfaces with curvatures defined by
cosine functions.
13. The structure of claim 12 wherein the first arm and the second
arm are aligned along the first longitudinal axis, and the third
arm and the fourth arm are aligned along a second longitudinal axis
that is transverse to the first longitudinal axis.
14. A structure comprising: a first waveguide crossing including a
first central section, a first plurality of arms aligned along a
first longitudinal axis, and a second plurality of arms aligned
along a second longitudinal axis that is oriented transverse to the
first longitudinal axis, each of the first plurality of arms and
the second plurality of arms connected to a different portion of
the first central section; and a second waveguide crossing
including a second central section and a third plurality of arms,
each of the third plurality of arms connected to a different
portion of the second central section, at least one of the third
plurality of arms positioned over one of the first plurality of
arms, and at least one of the third plurality of arms positioned
over one of the second plurality of arms, wherein the first
waveguide crossing is comprised of a first material, and the second
waveguide crossing is comprised of a second material that is
different in composition from the first material.
15. The structure of claim 14 wherein the second central section of
the second waveguide crossing positioned over the first central
section of the first waveguide crossing, and each of the third
plurality of arms respectively terminates at an end that is located
over either one of the first plurality of arms or one of the second
plurality of arms.
16. A method comprising: patterning a layer of material to define a
first waveguide core and a waveguide crossing including a central
section and a first arm positioned between the first waveguide core
and the central section, wherein the first arm and the first
waveguide core are aligned along a longitudinal axis, the first arm
is coupled to the first waveguide core at a first interface, the
first arm is coupled to a first portion of the central section at a
second interface, the first arm has a first width at the first
interface, a second width at the second interface, and a third
width between the first interface and the second interface, the
third width is greater than the first width, and the third width is
greater than the second width.
17. The method of claim 16 wherein the first width is less than the
second width.
18. The method of claim 16 wherein the first arm has a side surface
with a curvature defined by a cosine function.
19. The method of claim 16 wherein the first width and the second
width are unequal, and the third width is asymmetrically located
along the longitudinal axis between the first interface and the
second interface.
20. The method of claim 16 wherein the layer of material is
patterned to define a second waveguide core and a second arm of the
waveguide crossing, the second arm has a third interface coupled to
the second waveguide core and a fourth interface coupled to a
second portion of the central section, the first arm has a first
side surface with a first curvature defined by a first cosine
function, the second arm has a second side surface with a second
curvature defined by a second cosine function, and the first
curvature is substantially identical to the second curvature.
Description
BACKGROUND
The present invention relates to photonics chips and, more
specifically, to structures for a waveguide crossing and methods of
fabricating a structure for a waveguide crossing.
Photonics chips are used in many applications and systems
including, but not limited to, data communication systems and data
computation systems. A photonics chip integrates optical
components, such as waveguides, optical switches, directional
couplers, and bends, and electronic components, such as
field-effect transistors, into a unified platform. Among other
factors, layout area, cost, and operational overhead may be reduced
by the integration of both types of components on the same
chip.
A waveguide crossing is building block used in photonics chips to
provide paths for propagating optical signals. A waveguide crossing
is an optical element in which two waveguide cores in a single
layer intersect and directly cross. An ideal waveguide crossing may
be designed with measures to provide high transmission in each
straight path and low crosstalk to the corresponding crossing path.
However, despite these measures, waveguide cores may unwantedly
exhibit high insertion loss and high cross-talk. In addition,
waveguide crossings possess large footprints that may hamper dense
integration in a photonics chip.
Improved structures for a waveguide crossing and methods of
fabricating a structure for a waveguide crossing are needed.
SUMMARY
In an embodiment of the invention, a structure includes a waveguide
crossing including a central section and an arm positioned between
a waveguide core and the central section. The arm and the waveguide
core are aligned along a longitudinal axis. The arm is coupled to
the waveguide core at a first interface, and the arm is coupled to
a portion of the central section at a second interface. The arm has
a first width at the first interface, a second width at the second
interface, and a third width between the first interface and the
second interface. The third width is greater than the first width,
and the third width greater than the second width.
In an embodiment of the invention, a structure includes a first
waveguide crossing having a first central section and a first
plurality of arms connected to the first central section. The
structure further includes a second waveguide crossing positioned
over the first waveguide crossing. The second waveguide crossing
includes a second central section and a second plurality of arms
connected to the second central section. The first waveguide
crossing is comprised of a first material, and the second waveguide
crossing is comprised of a second material that is different in
composition from the first material.
In an embodiment of the invention, a method includes patterning a
layer of material to define a waveguide core and a waveguide
crossing that includes a central section and an arm positioned
between the waveguide core and the central section. The arm and the
waveguide core are aligned along a longitudinal axis. The arm is
coupled to the waveguide core at a first interface, and the arm is
coupled to a portion of the central section at a second interface.
The arm has a first width at the first interface, a second width at
the second interface, and a third width between the first interface
and the second interface. The third width is greater than the first
width, and the third width is greater than the second width.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are incorporated in and constitute
a part of this specification, illustrate various embodiments of the
invention and, together with a general description of the invention
given above and the detailed description of the embodiments given
below, serve to explain the embodiments of the invention. In the
drawings, like reference numerals refer to like features in the
various views.
FIG. 1 is a diagrammatic top view of a structure at an initial
fabrication stage of a processing method in accordance with
embodiments of the invention.
FIG. 2 is an enlarged view of a portion of FIG. 1.
FIG. 3 is a cross-sectional view taken generally along line 3-3 in
FIG. 1.
FIG. 4 is a cross-sectional view of the structure at a fabrication
stage of the processing method subsequent to FIG. 3.
FIGS. 5-7 are cross-sectional views of structures in accordance
with alternative embodiments of the invention.
FIG. 8 is a cross-sectional view of a structure in accordance with
alternative embodiments of the invention.
FIG. 8A is a top view of a structure in which FIG. 8 is taken
generally along line 8-8 and in which layers are omitted for
purposes of clarity of description.
FIG. 9 is a cross-sectional view of a structure in accordance with
alternative embodiments of the invention.
DETAILED DESCRIPTION
With reference to FIGS. 1-3 and in accordance with embodiments of
the invention, a structure 10 includes a waveguide crossing 12, a
waveguide core 14 and a waveguide core 16 that are coupled to
respective arms 22, 24 of the waveguide crossing 12 to respectively
provide an input port and a through port, and a waveguide core 18
and a waveguide core 20 that are coupled to respective arms 26, 28
of the waveguide crossing 12 to provide a cross port. The waveguide
crossing 12 includes a central section 30 providing a junction that
is arranged between the arms 22, 24 of the waveguide crossing 12
along the longitudinal axis 15, and also arranged between the arms
26, 28 of the waveguide crossing 12 along the longitudinal axis 19.
Each of the arms 22, 24, 26, 28 is coupled to a different portion
of the central section 30. The waveguide cores 14, 16 and the arms
22, 24 of the waveguide crossing 12 are aligned along a
longitudinal axis 15, and the waveguide cores 18, 20 and the arms
26, 28 of the waveguide crossing 12 are aligned along a
longitudinal axis 19 that is oriented transverse to the
longitudinal axis 15 of the waveguide cores 14, 16. In an
embodiment, the longitudinal axes 15, 19 may be oriented orthogonal
to each other.
The waveguide crossing 12 and the waveguide cores 14, 16, 18, 20
may be composed of single-crystal semiconductor material (e.g.,
single-crystal silicon). The waveguide crossing 12 and the
waveguide cores 14, 16, 18, 20 may be formed by patterning a device
layer of a silicon-on-insulator (SOI) wafer with lithography and
etching processes that form an etch mask over the device layer and
etch the masked device layer with an etching process, such as
reactive ion etching (ME), in which the buried insulator layer 32
functions as an etch stop. The waveguide crossing 12 and the
waveguide cores 14, 16, 18, 20 may be arranged on a buried
insulator layer 32 of the SOI wafer. The buried insulator layer 32
may be composed of a dielectric material, such as silicon dioxide,
and buried insulator layer 32 is arranged over a substrate 34 that
may contain single-crystal semiconductor material (e.g.,
single-crystal silicon). The waveguide crossing 12 and the
waveguide cores 14, 16, 18, 20 may have a ridge construction. The
buried insulator layer 32 may operate as a lower cladding providing
confinement for the waveguide crossing 12 and the waveguide cores
14, 16, 18, 20 of the structure 10.
Each of the arms 22, 24, 26, 28 may have shapes with curvatures
that are identical or substantially identical with respect to the
central section 30 other than orientation along the respective
longitudinal axis 15, 19. The arms 22, 24, 26, 28 are subsequently
discussed in connection with the arm 22 with an understanding that
the subsequent discussion applies equally to the arms 24, 26,
28.
The arm 22 has an interface 36 with the waveguide core 14 defining
an input to the arm 22, and the arm 22 has an interface 38 with the
central section 30 defining an output from the arm 22. The arm 22
has a width, W1, at the interface 36 with the waveguide core 14, a
width, W2, at the interface 38 with the central section 30, and a
maximum width, Wmax, that is located along the longitudinal axis 15
between the interface 36 and the interface 38. The location of the
maximum width between the interfaces 36, 38 differs from a
conventional taper or inverse taper in which the maximum width
occurs at either the beginning or end of the taper. The maximum
width, Wmax, is greater than the width, W1, at the interface 36
with the waveguide core 14 and the width, W2, at the interface 38
with the central section 30. The central section 30 is square in
shape with the width of each side equal to the width, W2.
The arm 22 extends along a total length, L, along the longitudinal
axis 15 between the interface 36 and the interface 38. The arm 22
has a section positioned between the interface 36 and the location
of the maximum width, Wmax. The total length, L, is divided into a
length, L1, of the section positioned between the location of the
maximum width, Wmax, and the interface 36 and a length, L2, of the
section positioned between the location of the maximum width, Wmax,
and the interface 38. In an embodiment in which the width, W1, at
the interface 36 and the width, W2, at the interface 38 are
unequal, the location of the maximum width, Wmax, is asymmetrically
positioned between the interface 36 and the interface 38. For
example, if the width, W1, at the interface 36 with the waveguide
core 14 is less than the width, W2, at the interface 38 with the
central section 30, then the value of the length, L1 is greater
than the value of the length, L2, such that the location of the
maximum width, Wmax, is closer to the interface 38 with the central
section 30 than to the interface 36 with the waveguide core 14. In
an embodiment in which the width, W1, at the interface 36 and the
width, W2, at the interface 38 are equal, the location of the
maximum width, Wmax, may be symmetrically positioned between the
interface 36 and the interface 38.
The shape of the arm 22 has an envelope at its side surfaces 23
with a curvature at each of its side surfaces 23 that may be
described by a non-linear function. In an embodiment, the shape of
the arm 22 has an envelope at its side surfaces 23 with a curvature
at each of its side surfaces 23 that may be described by a cosine
function. Specifically, the width of the shape for the arm 22 as a
function of position, x, along the longitudinal axis 15 may be
given by W(x)=Wmax.cndot. cos(.pi.x/2L0) wherein L0 is the position
along the longitudinal axis 15 that the cosine curve converges at
and crosses the longitudinal axis 15 (i.e., W=0). The maximum
width, Wmax, of the curvature occurs at x=0. In an alternative
embodiment, the width of the shape of the arm 22 as a function of
position along the longitudinal axis 15 may be described by a sine
function W(x)=Wmax.cndot. sin(.pi.x/2L) defining the curvature of
the envelope.
Given a set of widths, W1, W2, Wmax, values may be calculated for
the lengths L1 and L2 of the different sections of the arm 22. The
length, L1, is dependent on a ratio of the width, W1, to the width,
Wmax, and the length, L2, is dependent on a ratio of the width, W2,
to the width, Wmax. Specifically, the absolute value of L1 is equal
to (2L0/.pi.).cndot.arccos (W1/Wmax), and the absolute value of L2
is equal to (2L0/.pi.).cndot.arccos (W2/Wmax).
The total length, Ltotal, of the waveguide crossing 12 along the
set of arms 22, 24 between the interface 36 of the arm 22 with the
waveguide core 14 and the interface 36 of the arm 24 with the
waveguide core 16 is equal to (2.cndot.L)+W2. Similarly, the total
length of the waveguide crossing 12 along the set of arms 26, 28
between the interface 36 of the arm 26 with the waveguide core 18
and the interface 36 of the arm 28 with the waveguide core 20 is
also equal to (2.cndot.L)+W2. Consequently, the waveguide crossing
12 has a rotational symmetry of the order four (4).
The waveguide crossing 12 has a compact footprint due to the
non-linear curved shapes of the arms 22, 24, 26, 28. The waveguide
crossing 12 may be characterized by low insertion loss, low
cross-talk, low reflection, and low wavelength dependency also due
to the non-linear curved shapes of the arms 22, 24, 26, 28. The
waveguide crossing 12 may be optimized for the O-band (1260 nm to
1360 nm) and may be optimized for transmitting optical signals with
transverse electric (TE) polarization.
With reference to FIG. 4 in which like reference numerals refer to
like features in FIG. 3 and at a subsequent fabrication stage,
dielectric layers 40, 42, 44, 46 composed of respective dielectric
materials are sequentially formed in a layer stack over the
waveguide crossing 12 and the waveguide cores 14, 16, 18, 20. In
the layer stack, the dielectric layer 40 is arranged over the
buried insulator layer 32, the waveguide crossing 12 and the
waveguide cores 14, 16, 18, 20, the dielectric layer 42 is arranged
over the dielectric layer 40, the dielectric layer 44 is arranged
over the dielectric layer 42, and the dielectric layer 46 is
arranged over the dielectric layer 44. The waveguide crossing 12
and the waveguide cores 14, 16, 18, 20 are embedded or buried in
the dielectric material of the dielectric layer 40, which acts as
lateral cladding.
The dielectric layer 40 may be composed of a dielectric material,
such as silicon dioxide, deposited by chemical vapor deposition and
planarized with, for example, chemical mechanical polishing to
remove topography. The dielectric layer 42 may be composed of
dielectric material, such as silicon dioxide, deposited by chemical
vapor deposition or atomic layer deposition over the dielectric
layer 40. The dielectric layer 44 may be composed of dielectric
material, such as silicon nitride, deposited by chemical vapor
deposition or atomic layer deposition over the dielectric layer 42.
The dielectric layer 46 may be composed of dielectric material,
such as silicon dioxide, deposited by chemical vapor deposition or
atomic layer deposition over the dielectric layer 44. The
dielectric layers 42, 44, 46 may be planar layers arranged in the
layer stack over the planarized top surface of the dielectric layer
40.
A dielectric layer 48 of a contact level is formed by
middle-of-line processing over the dielectric layer 46. The
dielectric layer 48 may be composed of dielectric material, such as
silicon dioxide, deposited by chemical vapor deposition using ozone
and tetraethylorthosilicate (TEOS) as reactants.
A back-end-of-line stack, generally indicated by reference numeral
50, is formed by back-end-of-line processing over the dielectric
layer 48 and the structure 10. The back-end-of-line stack 50 may
include one or more interlayer dielectric layers composed of one or
more dielectric materials, such as a carbon-doped silicon oxide,
and metallization composed of, for example, copper, tungsten,
and/or cobalt that is arranged in the one or more interlayer
dielectric layers.
The structure 10, in any of its embodiments described herein, may
be integrated into a photonics chip 60 (FIG. 1) that may include
electronic components 52 and optical components 54 in addition to
the waveguide crossing 12 and the waveguide cores 14, 16, 18, 20.
The electronic components 52 may include, for example, field-effect
transistors that are fabricated by CMOS front-end-of-line (FEOL)
processing using the device layer of the SOI wafer.
With reference to FIG. 5 in which like reference numerals refer to
like features in FIG. 2 and in accordance with alternative
embodiments of the invention, the device layer may be partially
etched adjacent to sidewalls of the waveguide crossing 12 and the
waveguide cores 14, 16, 18, 20 during patterning to define a slab
layer 56. The slab layer 56, which is in direct contact with the
buried insulator layer 32, is coupled to the waveguide crossing 12
and the waveguide cores 14, 16, 18, 20. The slab layer 56 is
thinner than the waveguide crossing 12 and the waveguide cores 14,
16, 18, 20, which are masked during the patterning forming the slab
layer 56. The waveguide crossing 12 and the waveguide cores 14, 16,
18, 20 may have a rib construction due to the addition of the slab
layer 56.
With reference to FIG. 6 and in accordance with alternative
embodiments of the invention, the waveguide crossing 12 and the
waveguide cores 14, 16, 18, 20 may be composed of a different
material and may be located over the dielectric layer 46 and
embedded in dielectric layer 48. In an embodiment, the waveguide
crossing 12 may be composed of a dielectric material, such as
silicon nitride. The waveguide crossing 12 and the waveguide cores
14, 16, 18, 20 may be formed by depositing a layer of the
dielectric material on the dielectric layer 46, and then patterning
the deposited layer with lithography and etching processes that
lithographically form an etch mask over the deposited layer and
etch the masked deposited layer with an etching process, such as
reactive ion etching (RIE).
With reference to FIG. 7 in which like reference numerals refer to
like features in FIG. 6 and in accordance with alternative
embodiments of the invention, the deposited layer may be partially
etched adjacent to sidewalls of the waveguide crossing 12 and the
waveguide cores 14, 16, 18, 20 during patterning to define a slab
layer 58. The slab layer 58, which is in direct contact with the
dielectric layer 46, is coupled to the waveguide crossing 12 and
the waveguide cores 14, 16, 18, 20. The slab layer 58 is thinner
than the waveguide crossing 12 and the waveguide cores 14, 16, 18,
20, which are masked during patterning. The waveguide crossing 12
and the waveguide cores 14, 16, 18, 20 may have a rib construction
due to the addition of the slab layer 58.
With reference to FIGS. 8, 8A in which like reference numerals
refer to like features in FIG. 4 and in accordance with alternative
embodiments of the invention, the structure 10 may further include
a waveguide crossing 66 that is disposed over the waveguide
crossing 12. The arms 68 of the waveguide crossing 66 may be
located in a vertical direction over (i.e., above in the
y-direction) the arms 22, 24, 26, 28 of the waveguide crossing 12
in a stacked relationship. In an embodiment, the arms 68 of the
waveguide crossing 66 may have the same shape as the arms 22, 24,
26, 28 of the waveguide crossing 12 with interfaces similar to
interfaces 36, 38, as well as a central section 70 that is similar
to central section 30 of the waveguide crossing 12. The arms 68 of
the waveguide crossing 66 may terminate at respective ends 72 that
are analogous to the interfaces 36 of the arms 22, 24, 26, 28 of
the waveguide crossing 12 and each ends 72 may terminate over one
of the arms 22, 24, 26, 28 of the waveguide crossing 12.
The waveguide crossing 66 may be composed of a material having a
different composition than the material from which the waveguide
crossing 12 is composed. In an embodiment, the arms 68 of the
waveguide crossing 66 may be composed of a dielectric material,
such as silicon nitride, and the arms of the waveguide crossing 12
may be composed of a single-crystal semiconductor material, such as
single-crystal silicon. In an alternative embodiment and as shown
in FIG. 9, the arms 68 of the waveguide crossing 66 may be composed
of a polycrystalline semiconductor material (e.g., polycrystalline
silicon), and the arms of the waveguide crossing 12 may be composed
of a single-crystal semiconductor material, such as single-crystal
silicon.
Generally, the waveguide crossing 12 and the waveguide crossing 66
are composed of respective materials of different composition and
define a bilayer or multiple-layer stack of the different
materials. The addition of the waveguide crossing 66 over the
waveguide crossing 12 may function to improve the performance of
the waveguide crossing 12. For example, insertion loss may be
reduced by the addition of the waveguide crossing 66 over the
waveguide crossing 12.
In alternative embodiments, the waveguide crossing 66 of FIG. 8 may
be arranged over the waveguide crossing 12 of FIG. 6 or FIG. 7. In
alternative embodiments, the waveguide crossing 66 of FIG. 8 may be
arranged beneath the waveguide crossing 12 of FIG. 6 or FIG. 7. In
alternative embodiments, the waveguide crossing 66 of FIG. 8 may be
arranged beneath the waveguide crossing 12 of FIG. 6 or FIG. 7, and
the waveguide crossing 66 may be composed of a single-crystal
semiconductor material, such as single-crystal silicon. In
alternative embodiments, one or more waveguide crossings 66 may be
arranged above and beneath the waveguide crossing 12 of FIG. 6 or
FIG. 7.
In alternative embodiments, the waveguide crossing 66 of FIG. 8 may
be arranged over the waveguide crossing 66 of FIG. 9 such that both
waveguide crossings 66 are arranged over the waveguide crossing 12
of FIG. 4 or FIG. 5. In alternative embodiments, an additional
waveguide crossing (not shown) may be formed from the
single-crystal semiconductor material of the device layer and may
be arranged beneath the waveguide crossing 12 of FIG. 6 or FIG. 7
in addition to the waveguide crossing 66 of FIG. 8 to provide a
three-layer layer stack. In alternative embodiments, the waveguide
crossing 66 of FIG. 8 and the waveguide crossing 66 of FIG. 9 may
be added to the waveguide crossing 12 of FIG. 6 or FIG. 7 to
provide a three-layer stack.
The methods as described above are used in the fabrication of
integrated circuit chips. The resulting integrated circuit chips
can be distributed by the fabricator in raw wafer form (e.g., as a
single wafer that has multiple unpackaged chips), as a bare die, or
in a packaged form. The chip may be integrated with other chips,
discrete circuit elements, and/or other signal processing devices
as part of either an intermediate product or an end product. The
end product can be any product that includes integrated circuit
chips, such as computer products having a central processor or
smartphones.
References herein to terms modified by language of approximation,
such as "about", "approximately", and "substantially", are not to
be limited to the precise value specified. The language of
approximation may correspond to the precision of an instrument used
to measure the value and, unless otherwise dependent on the
precision of the instrument, may indicate +/-10% of the stated
value(s).
References herein to terms such as "vertical", "horizontal", etc.
are made by way of example, and not by way of limitation, to
establish a frame of reference. The term "horizontal" as used
herein is defined as a plane parallel to a conventional plane of a
semiconductor substrate, regardless of its actual three-dimensional
spatial orientation. The terms "vertical" and "normal" refer to a
direction perpendicular to the horizontal, as just defined. The
term "lateral" refers to a direction within the horizontal
plane.
A feature "connected" or "coupled" to or with another feature may
be directly connected or coupled to or with the other feature or,
instead, one or more intervening features may be present. A feature
may be "directly connected" or "directly coupled" to or with
another feature if intervening features are absent. A feature may
be "indirectly connected" or "indirectly coupled" to or with
another feature if at least one intervening feature is present. A
feature "on" or "contacting" another feature may be directly on or
in direct contact with the other feature or, instead, one or more
intervening features may be present. A feature may be "directly on"
or in "direct contact" with another feature if intervening features
are absent. A feature may be "indirectly on" or in "indirect
contact" with another feature if at least one intervening feature
is present.
The descriptions of the various embodiments of the present
invention have been presented for purposes of illustration but are
not intended to be exhaustive or limited to the embodiments
disclosed. Many modifications and variations will be apparent to
those of ordinary skill in the art without departing from the scope
and spirit of the described embodiments. The terminology used
herein was chosen to best explain the principles of the
embodiments, the practical application or technical improvement
over technologies found in the marketplace, or to enable others of
ordinary skill in the art to understand the embodiments disclosed
herein.
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